Gas turbine engine blades, and particularly fan blades of turbofan engines, experience foreign object damage (FOD) and erosion, as well as corrosion in some instances. Methods exist that can be used to improve FOD resistance, for example by increasing blade leading edge thickness, and to improve erosion resistance, for example by physical vapour deposition (PVD) coating or by chemical vapour deposition (CVD) coating, or a bonded metal sheath. However, each of the known processes has its disadvantages and limitations due to fatigue debits, reduced airfoil aerodynamic efficiency, manufacturing capabilities and durability. Field blending and leading edge (LE) restoration of the fan blade is also often required, as LE wear tends to degrade aerodynamic performance.
In addition, conventional titanium alloy aero-turbine engine fan blades have high density and cost relative to aluminium alloys and carbon fiber reinforced polymer composites. Fan blades made from high density materials such as titanium alloys significantly increase the weight of the fan hub needed to support the centrifugal force of the rotating fan blades. Such high density fan blades also significantly increases the weight of the containment fan casing required and support structures needed to contain the high kinetic energy of a released fan blade in the event of blade failure that releases the whole fan blade from its root fixing. Carbon fiber reinforced polymer composite fan blades, on the other hand, require a thick blade leading, edge (relative to a solid titanium airfoil) as well as a metal leading edge sheath for protection from FOD and for erosion resistance. However such thick blade leading edges cause significant reduction in blade aerodynamic efficiency and thus a significant overall reduction in engine efficiency.
Therefore, there is a need for an aircraft engine fan blade which provides improved aerodynamic efficiency and durability, without compromising ease of maintenance and while being lightweight and thus helping with overall engine weight reduction and providing a cost saving.